Hyponatremia is a condition that occurs when the level of sodium in your blood is abnormally low. Sodium is an electrolyte, and it helps regulate the amount of water that's in and around your cells.

In hyponatremia, one or more factors — ranging from an underlying medical condition to drinking too much water during endurance sports — causes the sodium in your body to become diluted. When this happens, your body's water levels rise, and your cells begin to swell. This swelling can cause many health problems, from mild to life-threatening.

Hyponatremia treatment is aimed at resolving the underlying condition. Depending on the cause of hyponatremia, you may simply need to cut back on how much you drink. In other cases of hyponatremia, you may need intravenous fluids and medications.

Hyponatremia signs and symptoms may include:

Nausea and vomiting

Headache

Confusion

Loss of energy and fatigue

Restlessness and irritability

Muscle weakness, spasms or cramps

Seizures

Coma

When to see a doctor

If you have a medical condition that increases your risk of hyponatremia, or you have other risk factors for hyponatremia, such as participating in high-intensity activities, and you have the signs and symptoms of low blood sodium, see your doctor.

Sodium plays a key role in your body. It helps maintain normal blood pressure, supports the work of your nerves and muscles, and regulates your body's fluid balance.

A normal sodium level is between 135 and 145 milliequivalents per liter (mEq/L) of sodium. Hyponatremia occurs when the sodium in your blood falls below 135 mEq/L.

Many possible conditions and lifestyle factors can lead to hyponatremia, including:

Certain medications. Some medications, such as some water pills (diuretics), antidepressants and pain medications, can cause you to urinate or perspire more than normal.

Heart, kidney and liver problems. Congestive heart failure and certain diseases affecting the kidneys or liver can cause fluids to accumulate in your body, which dilutes the sodium in your body, lowering the overall level.

Syndrome of inappropriate anti-diuretic hormone (SIADH). In this condition, high levels of the anti-diuretic hormone (ADH) are produced, causing your body to retain water instead of excreting it normally in your urine.

Chronic, severe vomiting or diarrhea. This causes your body to lose fluids and electrolytes, such as sodium.

Drinking too much water. Because you lose sodium through sweat, drinking too much water during endurance activities, such as marathons and triathlons, can dilute the sodium content of your blood. Drinking too much water at other times can also cause low sodium.

Dehydration. Taking in too little fluid can also be a problem. If you get dehydrated, your body loses fluids and electrolytes.

The recreational drug Ecstasy. This amphetamine increases the risk of severe and even fatal cases of hyponatremia.

The following factors may increase your risk of hyponatremia:

Age. Older adults may have more contributing factors for hyponatremia, including age-related changes, taking certain medications and a greater likelihood of developing a chronic disease that alters the body's sodium balance.

Certain drugs. Medications that increase your risk of hyponatremia include thiazide diuretics as well as some antidepressants and pain medications. In addition, the recreational drug Ecstasy has been linked to fatal cases of hyponatremia.

Conditions that decrease your body's water excretion. Medical conditions that may increase your risk of hyponatremia include kidney disease, syndrome of inappropriate anti-diuretic hormone (SIADH) and heart failure, among others.

Intensive physical activities. People who drink too much water while taking part in marathons, ultramarathons, triathlons and other long-distance, high-intensity activities are at an increased risk of hyponatremia.

In chronic hyponatremia, sodium levels drop gradually over 48 hours or longer — and symptoms and complications are typically more moderate.

In acute hyponatremia, sodium levels drop rapidly — resulting in potentially dangerous effects, such as rapid brain swelling, which can result in coma and death.

Premenopausal women appear to be at the greatest risk of hyponatremia-related brain damage. This may be related to the effect of women's sex hormones on the body's ability to balance sodium levels.

Seek emergency care for anyone who develops severe signs and symptoms of hyponatremia, such as nausea and vomiting, confusion, seizures, or lost consciousness.

Call your doctor if you know you are at risk of hyponatremia and are experiencing nausea, headache, cramping or weakness. Depending on the extent and duration of these signs and symptoms, your doctor may recommend seeking immediate medical care.

If you have time to prepare, here's some information to help you get ready for your appointment, and what to expect from your doctor.

What you can do

List any symptoms you or your loved one has been experiencing and for how long.

Write down key medical information, including other medical problems for which you are being treated and the names of all medications, vitamins, supplements or other natural remedies you are taking.

Take a family member or friend along, if you are the one with symptoms of low blood sodium. Someone who accompanies you can help remember all of the information and provide support if you need immediate medical care.

Write down questions to ask your doctor.

For hyponatremia, some basic questions to ask your doctor include:

What's the most likely cause of my symptoms?

What causes hyponatremia?

How severe is the condition?

What treatment do you recommend?

How soon do you expect my symptoms will begin to improve?

Am I at risk of any long-term problems?

How can I prevent a recurrence of this condition?

Do I need to make any changes to how much fluid I usually drink?

What to expect from your doctor

Being ready to answer your doctor's questions may reserve time to go over any points you want to talk about in-depth. Your doctor may ask:

What are your symptoms and when did they start?

Have you started taking any new medications?

Have your symptoms been getting any better or worse since they first developed?

Have your symptoms included any mental changes, such as feeling confused, agitated or depressed?

Have you had nausea, vomiting or diarrhea?

Have you felt faint, had seizures or lost consciousness?

Have you had a headache? If yes, has it gotten progressively worse?

Have your symptoms included weakness, fatigue or lethargy?

Do you use recreational drugs? If yes, which drugs?

Your doctor will start by asking about your medical history and doing a physical examination.

However, because the signs and symptoms of hyponatremia occur in many conditions, it's impossible to diagnose the condition based on a physical exam alone. To confirm low blood sodium, your doctor will order blood tests and urine tests.

Hyponatremia treatment is aimed at addressing the underlying cause, if possible.

If you have moderate, chronic hyponatremia due to your diet, diuretics or drinking too much water, your doctor may recommend temporarily cutting back on fluids. He or she also may suggest adjusting your diuretic use to increase the level of sodium in your blood.

Intravenous fluids. Your doctor may recommend IV sodium solution to raise the sodium levels in your blood. This often requires a stay in the hospital.

Medications. You may take medications to manage the signs and symptoms of hyponatremia, such as headache, nausea and seizures.

The following measures may help you prevent hyponatremia:

Treat associated conditions. Getting treatment for conditions that contribute to hyponatremia, such as adrenal gland insufficiency, can help prevent low blood sodium.

Educate yourself. If you have a medical condition that increases your risk of hyponatremia or you take diuretic medications, be aware of the signs and symptoms of low blood sodium. Always talk with your doctor about the risks of a new medication.

Take precautions during high-intensity activities. Athletes should drink only as much fluid as they lose due to sweating during a race. Thirst is generally a good guide to how much water or other fluids you need.

Consider drinking sports beverages during demanding activities. Ask your doctor about replacing water with sports beverages that contain electrolytes when participating in endurance events such as marathons, triathlons and other demanding activities.

Drink water in moderation. Drinking water is vital for your health, so make sure you drink enough fluids. But don't overdo it. Thirst and the color of your urine are usually the best indications of how much water you need. If you're not thirsty and your urine is pale yellow, you are likely getting enough water.

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